Let f:R→Rf:\mathbb{R}\rightarrow \mathbb{R}f:R→R be defined by f(x)=x3+3x+1f(x) = x^3+3x+1f(x)=x3+3x+1 and ggg be the inverse of fff. If the value of g′′(5)g''(5) g′′(5) is equal to −ab\dfrac{-a}{b}b−a​, where aaa and bbb are coprime positive integers, find the value of a+ba+ba+b.